With the recent accelerated reduction in the size and weight of mobile information terminals such as cellphones, laptop computers and smartphones, there is a demand for higher capacities of batteries that power such devices. Nonaqueous electrolyte secondary batteries, which are charged and discharged by the movement of lithium ions between positive and negative electrodes, have a high energy density and a high capacity and are widely used as power supplies for driving the above mobile information terminals.
Further, nonaqueous electrolyte secondary batteries recently attract attention as power supplies for powering electric vehicles, electric tools and the like, and are expected to find a wider range of applications. Batteries as power supplies for such vehicles and electric tools are required to have a high capacity for long use and also to have excellent cycle characteristics. In particular, vehicle-mounted applications increasingly demand that not only cycle characteristics but also low-temperature characteristics be enhanced.
To realize batteries having a high capacity and excellent cycle characteristics, for example, Patent Literature 1 presents a nonaqueous secondary battery that includes a positive electrode which has a positive electrode mixture layer containing a Li transition metal oxide represented by the composition formula Li1+yMO2 (−0.3≤y≤0.3, M denotes two or more kinds of elements including Ni, and the percentage of Ni in M is 30 mol % to 95 mol %), a negative electrode which has a negative electrode mixture layer containing SiOx (0.5≤x≤1.5) and graphite, and a nonaqueous electrolyte, wherein the battery is configured so that the potential of the negative electrode when the battery is discharged to 2.5 V is not more than 1.0 V versus Li.